State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing100084, China.
Department of Nuclear Science and Engineering and Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts02139, United States.
Chem Rev. 2023 Jan 25;123(2):811-833. doi: 10.1021/acs.chemrev.2c00251. Epub 2022 Nov 18.
Recent progress in high-energy-density oxide cathodes for lithium-ion batteries has pushed the limits of lithium usage and accessible redox couples. It often invokes hybrid anion- and cation-redox (HACR), with exotic valence states such as oxidized oxygen ions under high voltages. Electrochemical cycling under such extreme conditions over an extended period can trigger various forms of chemical, electrochemical, mechanical, and microstructural degradations, which shorten the battery life and cause safety issues. Mitigation strategies require an in-depth understanding of the underlying mechanisms. Here we offer a systematic overview of the functions, instabilities, and peculiar materials behaviors of the oxide cathodes. We note unusual anion and cation mobilities caused by high-voltage charging and exotic valences. It explains the extensive lattice reconstructions at room temperature in both good (plasticity and self-healing) and bad (phase change, corrosion, and damage) senses, with intriguing electrochemomechanical coupling. The insights are critical to the understanding of the unusual self-healing phenomena in ceramics (e.g., grain boundary sliding and lattice microcrack healing) and to novel cathode designs and degradation mitigations (e.g., suppressing stress-corrosion cracking and constructing reactively wetted cathode coating). Such mixed ionic-electronic conducting, electrochemically active oxides can be thought of as almost "metalized" if at voltages far from the open-circuit voltage, thus differing significantly from the highly insulating ionic materials in electronic transport and mechanical behaviors. These characteristics should be better understood and exploited for high-performance energy storage, electrocatalysis, and other emerging applications.
近年来，高能量密度锂离子电池的氧化物阴极取得了重大进展，推动了锂的使用极限和可及的氧化还原对的发展。它通常涉及混合阴离子和阳离子氧化还原（HACR），在高电压下具有氧化氧离子等奇异的价态。在如此极端的条件下进行电化学循环会引发各种形式的化学、电化学、机械和微观结构降解，从而缩短电池寿命并引发安全问题。缓解策略需要深入了解其潜在机制。在这里，我们对氧化物阴极的功能、不稳定性和特殊材料行为进行了系统的综述。我们注意到高电压充电引起的异常阴离子和阳离子迁移率以及奇异的价态。这解释了在室温下广泛的晶格重构，既有好的（塑性和自修复）也有坏的（相转变、腐蚀和损坏），同时存在有趣的电化学机械耦合。这些见解对于理解陶瓷中的异常自修复现象（例如晶界滑动和晶格微裂纹愈合）以及新型阴极设计和降解缓解（例如抑制应力腐蚀开裂和构建反应性润湿阴极涂层）至关重要。这些混合离子-电子导电、电化学活性氧化物如果在远离开路电压的电压下，可被视为几乎“金属化”，因此在电子输运和机械行为方面与高度绝缘的离子材料有显著差异。这些特性应该得到更好的理解和利用，以实现高性能储能、电催化和其他新兴应用。
